1. Field of the Invention
This invention relates in general to aircraft landing gear, and more particularly, to a an automatic shock strut which shrinks in size when the landing gear is retracted into the fuselage of the aircraft and returns to a normally extended position after the landing gear extends from the fuselage of the aircraft.
2. Background of the Related Art
In the design and manufacture of aircraft, it is generally desirable to minimize the space required by components of the aircraft. One approach to saving space in aircraft is to shorten the length of landing gear when it is retracted into a stowed position in the aircraft. The shortening of the landing gear may be required by the initial design of an aircraft or may be desired in order to minimize design changes in future generations of an existing aircraft.
A previous attempt to shorten the overall length of a shock strut during retraction is described in U.S. Pat. No. 4,047,681 to Hartel. The disclosed invention provides for a shrinking aircraft landing gear strut including a mechanism for shortening the shock strut that reacts to the rotational movement of the shock strut when moving from the extended position to the retracted position. The mechanism is effective to force the shock strut piston to telescope into the shock strut cylinder of the shock strut. Disadvantages of the mechanism in the Hartel patent are that the shock strut piston is forced against the air pressure established in the shock strut, thereby placing undesirable stress on the shock strut sealing components. In addition, shrinking of the shock strut occurs throughout the movement of the landing gear from the extended position to the retracted position requiring the landing gear housing be somewhat larger than that which is necessary to store the landing gear. Still further, existing aircraft landing gear cannot be readily modified to incorporate such a configuration.
A number of systems have been proposed which avoid the actuator effort problem by the use of mechanically or electrically operated hydraulic valves that operate to relieve the pressure in the shock absorber during retraction. Systems which rely on valves to relieve the pressure have the disadvantage of adding to the weight, and complexity of the landing gear and retraction system. As a rule, designers seek to reduce the number of valves used in landing gear since valves tend to add to the number of possible failure points in the system. In addition, the accumulators that receive the pressurized fluid to relieve the pressure in the shock absorbing mechanism must also be accommodated, thereby decreasing the net space savings of the system.
Clearly there is a need in the art for a shock strut shrinking mechanism used with aircraft landing gear that requires a minimal number of parts enabling simpler installation and maintenance. There is also a need for a mechanism that is sufficiently compact so as to reduce linkage flexure. In addition, there is a need for a shock strut shrinking mechanism that requires a minimum number of airframe attachment points.